Converter with series inductor

ABSTRACT

A converter is provided. The converter is capable of generating a loading current at an output node. The converter includes a high efficiency power channel and a fast transient response channel. The high efficiency power channel and the fast transient response channel share an inductor that is coupled to the output node. The high efficiency power channel has an additional inductor that is connected in series with the inductor coupled to the output node.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 62/579,941, filed on Nov. 1, 2017 andentitled “Converter with Inductors in Series,” which is herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to converters, and in particular toconverters with high efficiency and fast transient performance.

BACKGROUND

A converter converts one voltage level (e.g., an input voltage Vin) toanother voltage level (e.g., an output voltage Vout). A converterincludes one or more inductors coupled to an output node of theconverter. A converting efficiency is determined by a ratio of an outputpower to a total power including the output power and power losses,e.g., conduction loss, switching loss and driving loss.

SUMMARY

Power converters with high efficiency and fast transient performance areprovided.

Some embodiments relate to a converter for generating a loading currentat an output node. The converter comprises a plurality of inductors anda plurality of power channels. The plurality of inductors comprise afirst inductor coupled to the output node. The plurality of powerchannels comprise first and second power channels. The first powerchannel comprises the first inductor. The second power channel comprisesthe first inductor. The first power channel has higher power efficiencythan the second power channel.

In some embodiments, the second power channel has a faster transientresponse than the first power channel.

In some embodiments, the first power channel comprises a second inductorthat is connected in series with the first inductor.

In some embodiments, the plurality of power channels comprise a thirdpower channel. The plurality of inductors comprise a third inductorcoupled to the output node. The third power channel comprises the thirdinductor.

In some embodiments, the first power channel has higher power efficiencythan the third power channel.

In some embodiments, the converter further comprises a plurality ofdrive circuits to drive the plurality of power channels; and a controlloop circuit to control the plurality of drive circuits.

In some embodiments, the first and second power channels are driven withsignals of 180 degree phase differences.

In some embodiments, the first power channel is enabled. The secondpower channel is enabled when a transient event occurs. The second powerchannel is synchronized with the first power channel when the secondpower channel is enabled.

In some embodiments, the first power channel operates most of the timefor a first loading condition. The second power channel operates most ofthe time for a second loading condition. The second loading condition isheavier than the first loading condition.

In some embodiments, for the first loading condition, the second powerchannel is off, or enabled for a short time.

In some embodiments, for the second loading condition, the first powerchannel is off, or enabled for a short time.

Some embodiments relate to a converter for generating a loading currentat an output node. The converter comprises a first inductor, a firstpower channel, and a second power channel. The first inductor is coupledto the output node, and has an inductance value. The first power channelcomprises the first inductor and a second inductor connected in serieswith the first inductor. The second inductor has an inductance value.The second power channel also comprises the first inductor.

In some embodiments, the converter further comprises a first drivecircuit to drive the first power channel, a second drive circuit todrive the second power channel, and a control loop circuit to controlthe first and second drive circuits based on an output voltage at theoutput node and a reference voltage.

In some embodiments, the control loop circuit is configured to determinea loading condition at the output node, and/or an occurrence of atransient event at the output node.

In some embodiments, a ratio of the inductance value of the secondinductor to the inductance value of the first inductor is greater than 2and less than 8.

In some embodiments, the first and second power channels are driven withsignals of 180 degree phase differences.

In some embodiments, the first power channel is enabled. The secondpower channel is enabled when a transient event occurs. The second powerchannel is synchronized with the first power channel when the secondpower channel is enabled.

In some embodiments, the first power channel operates most of the timefor a first loading condition. The second power channel operates most ofthe time for a second loading condition. The second loading condition isheavier than the first loading condition.

In some embodiments, for the first loading condition, the second powerchannel is off, or enabled for a short time. For the second loadingcondition, the first power channel is off, or enabled for a short time.

Some embodiments relate to a method for a converter configured togenerate a loading current at an output node of the converter. Themethod comprises measuring a loading condition of the converter;determining whether the loading condition is larger than a thresholdvalue; and operating a first power channel or a second power channelbased on the determined loading condition. The first power channel hashigher power efficiency than the second power channel.

The foregoing summary is provided by way of illustration and is notintended to be limiting.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. The accompanying drawings are not necessarily drawn to scale,with emphasis instead being placed on illustrating various aspects ofthe techniques and devices described herein.

FIG. 1 is a schematic diagram illustrating a converter, according tosome embodiments.

FIG. 2 is a flow chart illustrating a method of driving and controllingthe converter of FIG. 1, according to some embodiments.

FIG. 3 is a timing diagram illustrating a comparison, between theconverter of FIG. 1 and a conventional converter, of transient responsesof an output voltage (Vout) and inductor current (IL) when a loadingcurrent (ILoad) with a slew rate of 3 A/μs is desired, according to someembodiments.

FIG. 4 is a schematic diagram illustrating a comparison, between theconverter of FIG. 1 and a conventional converter, of efficiency curvesdepending on loading currents (ILoad), according to some embodiments.

FIG. 5 is a flow chart illustrating a method of driving and controllingthe converter of FIG. 1, according to some embodiments.

FIG. 6 is a timing diagram illustrating transient responses of theconverter of FIG. 1, according to some embodiments.

FIG. 7 is a timing diagram illustrating a comparison, between theconverter of FIG. 1 and a conventional converter, of transient responsesof an output voltage (Vout) and inductor current (IL) when a loadingcurrent (ILoad) with a slew rate of 3 A/μs is desired, according to someembodiments.

FIG. 8 is a flow chart illustrating a method of driving and controllingthe converter of FIG. 1, according to some embodiments.

FIG. 9A is a schematic diagram illustrating the converter of FIG. 1 whenan efficient power channel acts as an energy source, according to someembodiments.

FIG. 9B is a schematic diagram illustrating the converter of FIG. 1 whena fast power channel acts as an energy source, according to someembodiments.

FIG. 10 a timing diagram illustrating an output voltage (Vout), inductorvoltage across L1 (LX1), inductor voltage across L2 (LX2), inductorcurrent through L1 (IL1), inductor current through L2 (IL2), and currentthrough a fast power channel (ICH2) of the converter of FIG. 1,according to some embodiments.

FIG. 11 is a schematic diagram illustrating a multi-phase converter,according to some embodiments.

DETAILED DESCRIPTION

The inventors have recognized and appreciated a tradeoff for convertersbetween high power efficiency and fast transient response. Aconventional converter provide currents to a load through a single powerchannel via a single inductor. A larger inductance provides higherefficiency, whereas a smaller inductance provides faster transientresponse. Conventionally, the inductance value is selected to balance aconverter's power efficiency performance and transient responseperformance.

The inventors have also recognized and appreciated that differentinductance values are better under different loading conditions. Onefactor of the power loss of the converter is the resistance values ofthe inductor, which has two types of resistance values: an AC resistance(ACR) value and a DC resistance (DCR) value. Both of the resistancevalues influence the efficiency of the converter. When the loading ofthe converter is small (that is, the loading current is small), thepower loss induced by the ACR value of the inductor dominates the powerloss of the converter. In this case, it is desired for the inductor tohave a large inductance value to decrease the ripple on the inductorcurrent flowing through the inductor, thereby getting higher efficiencyfor the converter. On the other hand, when the loading of the converteris large (that is, the loading current is large), the power loss inducedby the DCR value of the inductor dominates the power loss. At this time,it is desired for the inductor to have a small inductance value todecrease the average value of the inductor current flowing through theinductors, thereby getting higher efficiency for the converter.

The inventors have recognized and appreciated that a converter can haveboth high efficiency and fast transient response by having at least twopower channels, which may have different power conversion efficienciesand responses times. In some embodiments, a converter may have first andsecond power channels, both of which include a first inductor that iscoupled to an output node. The first power channel may have higher powerconversion efficiency than the second power channel, and thus may bereferred to as an efficient power channel. The efficient power channelmay include a second inductor that is connected in series with the firstinductor. The second power channel may have faster transient responsethan the first power channel, and thus may be referred to as a fastpower channel. The fast power channel may share at least the firstinductor with the efficient power channel. In some embodiments, the fastpower channel may include no inductors other than the first inductor.

FIG. 1 depicts a converter 100, according to some embodiments. Theconverter 100 may convert an input voltage VIN to an output voltage Voutat an output node 102 to drive a load, which may be coupled to theoutput node 102. The value of the load may change depending on, forexample, an operation mode of a system driven by the output voltageVout. For example, the output voltage Vout may drive a smartphone, whichmay operate in an active mode corresponding to a heavy loadingcondition, or a standby mode corresponding to a light loading condition.

The converter 100 may include a first power channel 104 and a secondpower channel 106. The first power channel may include transistors A, B,a first inductor L1, and a second inductor L2 in series with the firstinductor L1. The second inductor L2 may be coupled to the output node102. The first inductor L1 may be coupled to the second inductor L2,such that it is coupled to the output node 102 via the second inductorL2. The second power channel may include transistors C, D and the secondinductor L2. The transistors C, D may be configured similar totransistors A, B, for example, having the same gate lengths and widths.

The first and second inductors L1, L2 may be implemented by any suitableway, for example, to accommodate available footprint of an integratedcircuit (IC). In some embodiments, inductors L1, L2 may be formed asdiscrete components. In some embodiments, L1, L2 may be integratedinductors, such as on-chip spiral inductors. In some embodiments,inductors L1, L2 may each be a portion of a single inductor.

In some embodiments, L1 may have a larger inductance than L2. In someembodiments, a ratio of the L1's inductance to L2's inductance may begreater than 1 and less than 10, such as greater than 2 and less than 8,including, for example, greater than 3 and less than 5, such as 4, forexample. However, this is by way of illustration, as in some embodimentsthe ratio of inductances may be in a different range.

The first power channel 104 may have higher efficiency than the secondpower channel, and may be referred to as an efficient power channel. Thesecond power channel 106 may have faster transient response than thefirst power channel, and may be referred to as a fast power channel.

The converter 100 may include a first drive and control circuit 108, asecond drive and control circuit 110, and a control loop circuit 112 tocontrol the first and second drive and control circuits 108, 110. Thefirst and second drive and control circuits 108, 110 may drive andcontrol the first and second power channels 104, 106, respectively. Insome embodiments, drive and control circuits 108, 110 may be one driveand control circuit that is shared by both the first and second powerchannels 104, 106.

In some embodiments, the first drive and control circuit 108 may includea drive circuit to drive the first power channel 104. The first driveand control circuit 108 may also include a control circuit that may beprogrammed with instructions to control the first power channel 104 to,for example, switch between the input voltage VIN and a low voltage(e.g., ground) at a first switching frequency.

In some embodiments, the second drive and control circuit 110 mayinclude a drive circuit to drive the second power channel 106. Thesecond drive and control circuit 110 may also include a control circuitthat may be programmed with instructions to control the second powerchannel 106 to, for example, switch between the input voltage VIN and alow voltage (e.g., ground) at a second switching frequency. In someembodiments, the second switching frequency may be less than the firstswitching frequency (e.g., method 500 as illustrated in FIG. 5). In someembodiments, the second switching frequency may be the same as the firstswitching frequency when the converter 100 operates in a steady state(e.g., method 800 as illustrated in FIG. 8).

The control loop circuit 112 may control the first and second drive andcontrol circuits 108, 110 by, for example, comparing a feedback from theoutput node 102 (e.g., the output voltage Vout) to a reference (e.g., areference voltage Vref). The comparison results may indicate a magnitudeof a load driven by the converter 100 and/or a transient event by theoutput node 102. A transient event may occur when the requirement of aloading current at the output node changes caused by, for example, achange of operation mode of a system driven by the converter 100. Insome embodiments, the control loop circuit may be a control circuit or aprocessor programmed with instructions for controlling the first andsecond drive and control circuits 108, 110. In some embodiments, thefirst and second drive and control circuits 108, 110 may be drivecircuits and have no control circuits. In these scenarios, the controlloop circuit 112 may control drive circuits 108, 110 and thus controlthe first and second power channels 104,

The converter 100 may function as a buck converter when either one ofthe first and second power channels is enabled. The converter 100includes two power channels sharing an inductor L2 in the illustratedexample, however, the present application should not be limited to twopower channels sharing one inductor. A converter may include anysuitable number of power channels sharing one or more inductors, forexample, to accommodate requirements of power efficiency and transientresponse. For example, a converter may include three power channelssharing one inductor that is coupled to an output node of the converter.

FIG. 2 is a flow chart illustrating a method 200 of driving andcontrolling the converter 100, according to some embodiments. The method200 may start from measuring (act 202) a loading condition of theconverter 100 is determined by, for example, the control loop circuit112. The method may include determining (act 204) whether the loadingcondition is larger than a threshold value. If the loading condition isdetermined larger than the threshold value, the loading condition may beconsidered as a heavy loading condition. If the loading condition isdetermined smaller than the threshold value, the loading condition maybe considered as a light loading condition. In some embodiments, thethreshold value may be a threshold range, or an algorithm that isconfigured to determine the category of a loading condition.

The method 200 may further include, when the loading condition isdetermined as heavy, operating (act 206) a fast power channel (e.g., thesecond power channel 106) most of the time, for example, the probabilityof the fast power channel being in operation at a given time is greaterthan 50%, or greater than 70%, or greater than 90%, or any suitablepercentage. The method 200 may include, when the loading condition isdetermined as light, operating (act 208) an efficient power channel(e.g., the first power channel 104) most of the time, for example, theprobability of the efficient power channel being in operation at a giventime is greater than 50%, greater than 70%, or greater than 90%, or anysuitable percentage. During the heavy loading condition, although thefast power channel may operate most of the time, the efficient powerchannel may be turned off, or may be enabled for a short time, forexample, less than 50% of the time that the fast power channel operates,less than 30%, less than 10%, or any suitable percentage. During thelight loading condition, although the efficient power channel mayoperate most of the time, the fast power channel may be turned off, ormay be enabled for a short time, for example, less than 50% of the timethat the efficient power channel operates, less than 30%, less than 10%,or any suitable percentage.

FIG. 3 is a timing diagram illustrating a comparison, between theconverter 100 and a conventional converter, of transient responses of anoutput voltage (Vout) and inductor current (IL) when a loading current(ILoad) with a slew rate of 3 A/μs is desired, according to someembodiments. In the illustrated example, The conventional converter hasonly a single inductor of 0.47 μH, which is enabled all the time. On theother hand, the converter 100 has an L1 of 0.47 μH and an L2 of 0.22 μH.The converter 100 may be controlled by the method 200, which may measurethe Iload to determine a loading condition of the converter 100. It maybe determined that the loading condition is small before the increase ofIload. In this case, the efficient power channel may be enabled whilethe fast power channel may be disabled. When the Iload increases, it maybe determined that the loading condition becomes large. At this time,the fast power channel, which has faster transient response than theefficient power channel, may be enable. As a result, the converter 100reaches a desired Vout and IL faster than the conventional converter,and has less overshoot than the conventional converter.

FIG. 4 is a schematic diagram illustrating a comparison, between theconverter 100 and a conventional converter, of efficiency curvesdepending on loading currents (ILoad), according to some embodiments. Inthe illustrated example, the converter 100 and the conventionalconverter is configured similar to the illustrated example of FIG. 3.FIG. 4 shows that the converter 100 improves the converting efficiencyover the conventional converter by about 1.5% almost across the ILoadrange of 0.01 A to 5 A.

In some embodiments, a converter may have a peak efficiency higher than85%, higher than 88%, or higher than 92%. In some embodiments, aconverter may have an AC transient response that is faster than −25 mV,faster than −20 mV, or faster than −15 mV.

FIG. 5 is a flow chart illustrating a method 500 of driving andcontrolling the converter 100, according to some embodiments. The method500 may start from detecting (act 502) whether a transient event occursby, for example, the control loop circuit 112. The method 500 may alsoinclude enabling (act 504) a fast power channel (e.g., the second powerchannel 106) to be synchronized with an efficient power channel that isalready operating (e.g., the first power channel 104) when theoccurrence of a transient event is detected.

FIG. 6 is a timing diagram illustrating transient responses of theconverter 100 controlled by the method 500, according to someembodiments. Curve 602 illustrates an output loading current at theoutput node 102, which may include both the efficient power channelcurrent (e.g., the current flowing through the first power channel 104)and fast power channel current (e.g., the current flowing through thesecond power channel 106). In the illustrated example, an efficientpower channel is enabled before a detected transient event 604. Upon thedetection of an transient event 604, a fast power channel is enabled tosupport the transient event. The current flowing through the fast powerchannel, as illustrated by curve 606, contributes to the overall outputloading current illustrated by curve 602.

FIG. 7 is a timing diagram illustrating a comparison, between theconverter 100 and a conventional converter, of transient responses of anoutput voltage (Vout) and inductor current (IL) when a loading current(ILoad) with a slew rate of 3 A/μs is desired, according to someembodiments. In the illustrated example, the converter 100 has an L1 of0.47 μII and an L2 of 0.22 μH, and is controlled by the method 500. Theconventional converter has only a single inductor of 0.47 μH. FIG. 7shows that the converter reaches a desired Vout and IL faster than theconventional converter, and has less overshoot than the conventionalconverter.

FIG. 8 is a flow chart illustrating a method 800 of driving andcontrolling the converter 100, according to some embodiments. The method800 may interleave an efficient power channel (e.g., the first powerchannel 104) and fast power channel (e.g., the second power channel 106)by, for example, driving the efficient power channel and fast powerchannel with signals of a 180 degree phase difference.

In some embodiments, the method 800 may include a Phase I (act 802) whena fast power channel acts as an energy source, and an efficient powerchannel acts as a current sink, as illustrated in FIG. 9B. The method800 may also include a Phase II (act 804) when the efficient powerchannel acts as an energy source, and the fast power channel acts as acurrent sink, as illustrated in FIG. 9A.

The inventors have recognized and appreciated that the converter 100,controlled by the method 800, may have a higher efficiency than aconventional converter configured with a single power channel as thefast power channel of the converter 100. At the same time, thecontroverter 100, controlled by the method 800, may have a fastertransient response than a conventional converter configured with asignal power channel as the efficiency power channel of the converter100.

FIG. 10 a timing diagram illustrating an output voltage (Vout), inductorvoltage across L1 (LX1), inductor voltage across L2 (LX2), inductorcurrent through L1 (IL1), inductor current through L2 (IL2), and currentthrough a fast power channel (ICH2) of the converter 100, according tosome embodiments. In the illustrated example, during t1, a fast powerchannel acts as an energy source, and an efficient power channel acts asa current sink. During t2, the efficient power channel acts as an energysource, and the fast power channel acts as a current sink.

FIG. 11 is a schematic diagram illustrating a multi-phase converter1100, according to some embodiments. The converter 1100 may comprise aplurality of power channels 1112-1118, for providing an output voltageVout and/or an output loading current ILoad to an output node 1102. Theplurality of power channels may operate in different phases. Therefore,the converter 1100 may be referred to as a multi-phase converter.Although four power channels are illustrated in FIG. 11, it should beappreciated that a multi-phase converter 1100 may include any suitablenumber of power channels, such as three, five, or more.

The plurality of power channels 1112-1118 may each have an inductor thatis coupled to the output node 1102, for example, inductors L2-L4. Whilethe power channels 1114-1118 may each comprise a single inductor, thepower channel 1112 may comprise two inductors L1 and L2 connected inseries. The power channel 1112 may has a higher efficiency than thepower channel 1114, which may have a shorter response time than thepower channel 1112 when a transient event occurs at the output node1102. In some embodiments, the power channel 1112 may has the highestefficiency compared to the power channels 1114-1118. In those cases,each of inductors L3 and L4 may has an inductance value that is lessthan a sum of inductance values of inductors L1 and L2.

The converter 1100 may comprise a plurality of drive and controlcircuits 1104-1110 to drive and control the plurality of power channels1112-1118, respectively. A drive and control circuit may include a drivecircuit to drive a corresponding power channel. A drive and controlcircuit may also include a control circuit that may be programmed withinstructions to control a corresponding power channel to perform amethod, for example, method 200, method 500, or method 800.

The converter 1100 may comprise a control loop circuit 1120. The controlloop circuit 1120 may control the drive and control circuits 1104-1110by, for example, comparing a feedback from the output node 1102 (e.g.,the output voltage Vout) to a reference (e.g., a reference voltageVref). The comparison results may indicate a magnitude of a load drivenby the converter 1100 and/or a transient event at the output node 1102.In some embodiments, the control loop circuit may be a control circuitor a processor programmed with instructions for controlling the driveand control circuits 1104-1110.

Various aspects of the apparatus and techniques described herein may beused alone, in combination, or in a variety of arrangements notspecially discussed in the embodiments described in the foregoingdescription and is therefore not limited in its application to thedetails and arrangement of components set forth in the foregoingdescription or illustrated in the drawings. For example, aspectsdescribed in one embodiment may be combined in any manner with aspectsdescribed in other embodiments.

The terms “approximately”, “substantially,” and “about” may be used tomean within ±20% of a target value in some embodiments, within ±10% of atarget value in some embodiments, within ±5% of a target value in someembodiments, and yet within ±2% of a target value in some embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. A converter for generating a loading current atan output node, the converter comprising: a plurality of inductorscomprising a first inductor coupled to the output node; and a pluralityof power channels comprising first and second power channels, wherein:the first power channel comprises the first inductor, the second powerchannel comprises the first inductor, and the first power channel hashigher power efficiency than the second power channel.
 2. The converterof claim 1, wherein the second power channel has a faster transientresponse than the first power channel.
 3. The converter of claim 1,wherein the first power channel comprises a second inductor that isconnected in series with the first inductor.
 4. The converter of claim1, wherein: the plurality of power channels comprise a third powerchannel, the plurality of inductors comprise a third inductor coupled tothe output node, and the third power channel comprises the thirdinductor.
 5. The converter of claim 4, wherein the first power channelhas higher power efficiency than the third power channel.
 6. Theconverter of claim 1, further comprising: a plurality of drive circuitsto drive the plurality of power channels; and a control loop circuit tocontrol the plurality of drive circuits.
 7. The converter of claim 1,wherein the first and second power channels are driven with signals of180 degree phase differences.
 8. The converter of claim 1, wherein: thefirst power channel is enabled, the second power channel is enabled whena transient event occurs, and the second power channel is synchronizedwith the first power channel when the second power channel is enabled.9. The converter of claim 1, wherein: the first power channel operatesmost of the time for a first loading condition, and the second powerchannel operates most of the time for a second loading condition, thesecond loading condition being heavier than the first loading condition.10. The converter of claim 9, wherein: for the first loading condition,the second power channel is off, or enabled for a short time.
 11. Theconverter of claim 9, wherein: for the second loading condition, thefirst power channel is off, or enabled for a short time.
 12. A converterfor generating a loading current at an output node, the convertercomprising: a first inductor coupled to the output node and having aninductance value; a first power channel comprising the first inductorand a second inductor connected in series with the first inductor, thesecond inductor having an inductance value; and a second power channelcomprising the first inductor.
 13. The converter of claim 12, furthercomprising: a first drive circuit to drive the first power channel; asecond drive circuit to drive the second power channel; and a controlloop circuit to control the first and second drive circuits based on anoutput voltage at the output node and a reference voltage.
 14. Theconverter of claim 13, wherein the control loop circuit is configured todetermine a loading condition at the output node, and/or an occurrenceof a transient event at the output node.
 15. The converter of claim 12,wherein a ratio of the inductance value of the second inductor to theinductance value of the first inductor is greater than 2 and less than8.
 16. The converter of claim 12, wherein the first and second powerchannels are driven with signals of 180 degree phase differences. 17.The converter of claim 12, wherein: the first power channel is enabled,the second power channel is enabled when a transient event occurs, andthe second power channel is synchronized with the first power channelwhen the second power channel is enabled.
 18. The converter of claim 12,wherein: the first power channel operates most of the time for a firstloading condition, and the second power channel operates most of thetime for a second loading condition, the second loading condition beingheavier than the first loading condition.
 19. The converter of claim 18,wherein: for the first loading condition, the second power channel isoff, or enabled for a short time; and for the second loading condition,the first power channel is off, or enabled for a short time.
 20. Amethod for a converter configured to generate a loading current at anoutput node of the converter, the method comprising: measuring a loadingcondition of the converter; determining whether the loading condition islarger than a threshold value; and operating a first power channel or asecond power channel based on the determined loading condition, thefirst power channel having higher power efficiency than the second powerchannel.